Here's how Congress could kill the Iran deal

President Barack Obama, standing with Vice President Joe Biden, delivers remarks in the East Room of the White House, July 14, 2015, after an Iran nuclear deal is reached. AP Now that more than a year and a half of nuclear negotiations are in the books, attention on a signature legacy item for President Barack Obama now shifts to Congress.

Thanks to a bipartisan compromise that Obama ended up signing in May, Congress will have a say in the ultimate fate of the deal.

While even opponents of the deal concede the odds are long, there's at least a small chance that Congress could torpedo it.

"The American people are going to repudiate this and I believe Congress will kill the deal," said Sen. Tom Cotton (R-Arkansas), one of the more hawkish members of the Senate on foreign policy.

Here's a brief overview of what happens next:

Once Congress receives the details of the deal, it will have 60 days to debate and vote on it, according to the terms of the law Obama signed in May. A GOP congressional aide told Business Insider that it has not yet received the details.

If Congress sends a joint resolution of disapproval to Obama (meaning both chambers of Congress disapprove of the deal), it would trigger a new timeline. He would have 12 days to veto the resolution. That's likely, considering his promise Tuesday morning to veto anything that would hamper the deal's implementation.

Following an Obama veto, Congress would have 10 days to vote to override his veto, which would require a two-thirds majority of both chambers of Congress.

If both chambers vote to override, it would prevent Obama from suspending sanctions on Iran related to its nuclear program.

Simple math, then, is in favor of the Iran deal moving along through Congress unscathed.

Nevertheless, the deal has not only become just about universally unpopular among Republican members of Congress. It's also opposed by a chunk of Democrats normally aligned with Obama on both domestic- and foreign-policy matters.

Chuck Schumer. Susan Walsh/Associated Press Sen. Chuck Schumer (D-New York), the third-ranking Democrat in the Senate and the incoming Democratic leader after Sen. Harry Reid's retirement next year, said he'd be going through the deal with a "fine-toothed comb" before deciding whether or not to support it. Rep. Eliot Engel (D-New York), the top Democrat on the House Committee on Foreign Affairs, said likewise that he'd have to go through the details — but added that he's been "troubled" by the negotiations.

Many congressional observers consider it likely that Congress will pass an initial resolution of disapproval. Thereafter, it will again become another question of math.

"The rhetoric and behavior from Iran's ayatollahs has been so provocative in recent months that Congress is surprisingly united in its opposition to the nuclear deal that was announced this morning," said Greg Valliere, the chief political strategist at Potomac Research Group.

"Furious lobbying against the deal, from pro-Israeli groups in particular, will begin immediately as a 60-day review period starts. There's little doubt that both houses will pass a resolution of disapproval, which will prompt a veto from President Obama. Then the real drama will begin."

Angus King. AP A veto override would require at least 13 Democrats in the Senate and 44 in the House to break with their party and president — if all Republicans are united in their opposition.

There were 20 Democratic cosponsors of the legislation that eventually gave Congress a say in the negotiations. Some congressional GOP aides believe at least 13 of those Democrats and Sen. Angus King (I-Maine), an independent who caucuses with Democrats, are swayable.

GOP leaders aren't convinced they'll get the veto override — but they do plan to force a sustained drumbeat leading up to the first vote in September.

"This is going to be a tough sell," one House GOP aide told Business Insider. "Either you support the president's bad deal with Iran or you don't. There's gonna be no place to hide on this vote."